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The Role of Electrons in Icy Moon Exosphere Creation

Presentation #314.03 in the session Icy Satellites, Fields and Particles (Poster)

Published onOct 23, 2023
The Role of Electrons in Icy Moon Exosphere Creation

Planetary surfaces not protected by a sufficient atmosphere experience particle bombardment, which affects both surface chemical evolution and exosphere creation. Surface particles sputtered by irradiation either fall back onto the target surface, escape the gravitational bound of the target body, or become part of an exosphere. On Europa, H2O as well as radiolytically produced O2 and H2 are sputtered from the surface and are then dissociated and excited by incoming energetic particles. Hydrogen is light enough to dissipate into space and H2O falls back onto the surface, leaving behind an oxygen rich exosphere. Since Europa is not massive enough to retain its exosphere long term, the persistence of Europa’s O2 exosphere suggests it is constantly being replenished via sputtering.

Europa is the most heavily irradiated Galilean moon. While irradiating particles consist of ions, electrons, cosmic rays, etc., electrons contribute ~80% of the total energy striking Europa between 10 keV and 10 MeV. However, only a handful of experiments have studied electron induced sputtering under Europa-like conditions. One of those studies used a single electron energy to estimate that the global O2 production on Europa from electron irradiation was comparable to O2 production from all ionic irradiation components combined. Here we expand that work by studying electron-induced sputtering between energies of 0.5 and 10 keV and temperatures between 40 and 125 K relevant for icy bodies like Europa. Determining differences in the composition of material sputtered by ions and electrons is important in order to understand the role both particles play in exosphere creation/surface erosion and surface alteration of icy bodies.

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